Semiconductor chips become defective goods when performance degradation thereof above a certain level progresses due to use after shipment. It is considered that performance degradation due to use is caused by the lifetime (performance degradation appropriate to aging), or caused by incidental failure, and the like. However, when a semiconductor chip is determined as defective goods during maintenance and the like, it may be difficult to assess whether the defect thereof is caused by the lifetime (performance degradation appropriate to aging), or caused by incidental failure and the like.
On the other hand, the assessment of whether the cause of the performance degradation is caused by the lifetime or caused by incidental failure and the like is important from the viewpoint of feedback to the design. When the degree of progression of the performance degradation due to the lifetime of a semiconductor integrated circuit after shipment is understood in advance, this assessment can be realized with relative ease. In addition, when log information of the degree of progression of the performance degradation due to the lifetime is acquired, it is possible to anticipate the proper time for replacement of the semiconductor integrated circuit, and to make use of setting optimal maintenance time.
Here, as a method generally used in order to understand the degree of progression of the performance degradation due to the lifetime of the semiconductor integrated circuit, as disclosed in Non-Patent Document 1, there is a method of calculating the degree of degradation by constituting a ring oscillator using a CMOS circuit and detecting a change in the oscillation frequency thereof. The oscillation frequency can be digitally coded by using a counter, and a diagnosis of the degree of degradation can be performed with a simple configuration without using an external measuring instrument. In addition, in a technique disclosed in Non-Patent Document 1, the resolution of the degree of degradation in a utility area is improved by using two test and reference ring oscillators, thereby allowing the measurement time to be shortened.